目录
主要内容
代码分支
核心代码
BeanDefinitionReader
AbstractBeanDefinitionReader
XmlBeanDefinitionReader
测试
bean定义文件spring.xml
Java代码
测试结果
上一节加入了资源管理器,令我们的框架具备了读取配置文件的能力。在该篇文章中将为我们的框架加入xml格式的配置文件,在配置文件中声明式的定义bean信息,利用资源加载器读取xml配置文件,进而解析出bean信息,注入进bean容器。
BeanDefinitionReader:读取bean定义信息的接口,获取资源后,读取bean定义信息,生成BeanDefinition注册入容器。
AbstractBeanDefinitionReader:BeanDefinitionReader的抽象实现类,从需要实现的抽象类BeanDefinitionReader功能上看,该类需要拥有 ResourceLoader 和 BeanDefinitionRegistry 两个属性。
XmlBeanDefinitionReader:实现从xml中读取和加载Bean定义信息。
由于xml文件中读取的都是文本,本章节bean属性暂时只支持String类型和引用其他bean,后面会讲解类型转换器,实现类型转换。
注意:本章对BeanFactory的体系做了调整。
除去添加的核心代码外,其他地方也有非常细微的改动,想要测试代码可行性的同学可以查看该分支下具体代码。
定义加载资源并且读取Bean定义信息的接口方法,包括方法有:获取Bean注册表、获取资源加载器、从静态资源读取BeanDefinition,根据路径加载BeanDefinition。
Reader中加载的含义:reader的加载目标是资源下的Bean,不仅是read资源,还包括load Bean,registe Bean,即读取并注册,利用ResourceLoader加载资源后,读取Bean定义信息并注册到注册表。
public interface BeanDefinitionReader {
/**
* 获取注册表
* @return
*/
BeanDefinitionRegistry getRegistry();
/**
* 获取资源加载器
* @return
*/
ResourceLoader getResourceLoader();
void loadBeanDefinitions(Resource resource) throws BeansException;
void loadBeanDefinitions(String location) throws BeansException;
void loadBeanDefinitions(String[] locations) throws BeansException;
}
BeanDefinitionReader的抽象实现类
public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader{
private final BeanDefinitionRegistry registry;
private ResourceLoader resourceLoader;
protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {
this(registry, new DefaultResourceLoader());
}
@Override public BeanDefinitionRegistry getRegistry() {
return this.registry;
}
public AbstractBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
this.registry = registry;
this.resourceLoader = resourceLoader;
}
@Override public ResourceLoader getResourceLoader() {
return resourceLoader;
}
@Override public void loadBeanDefinitions(String[] locations) throws BeansException {
for (String location : locations) {
loadBeanDefinitions(location);
}
}
}
定义了一些字符常量表示xml节点名称,实现两个loadBeanDefinitions(),实现xml中BeanDefinition的读取和加载
package org.springframework.beans.factory.xml;
import cn.hutool.core.util.StrUtil;
import cn.hutool.core.util.XmlUtil;
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValue;
import org.springframework.beans.core.io.Resource;
import org.springframework.beans.core.io.ResourceLoader;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanReference;
import org.springframework.beans.factory.support.AbstractBeanDefinitionReader;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import java.io.IOException;
import java.io.InputStream;
/**
* ● @author: YiHui
* ● @date: Created in 17:41 2023/4/9
*/
public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {
public static final String BEAN_ELEMENT = "bean";
public static final String PROPERTY_ELEMENT = "property";
public static final String ID_ATTRIBUTE = "id";
public static final String NAME_ATTRIBUTE = "name";
public static final String CLASS_ATTRIBUTE = "class";
public static final String VALUE_ATTRIBUTE = "value";
public static final String REF_ATTRIBUTE = "ref";
public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
super(registry);
}
public XmlBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
super(registry, resourceLoader);
}
@Override public void loadBeanDefinitions(String location) throws BeansException {
ResourceLoader resourceLoader = getResourceLoader();
Resource resource = resourceLoader.getResource(location);
this.loadBeanDefinitions(resource);
}
@Override public void loadBeanDefinitions(Resource resource) throws BeansException {
try {
InputStream inputStream = resource.getInputStream();
doLoadBeanDefinitions(inputStream);
}catch (IOException e) {
throw new BeansException("IOException parsing XML document from " + resource, e);
}
}
private void doLoadBeanDefinitions(InputStream inputStream){
Document document = XmlUtil.readXML(inputStream);
Element rootElement = document.getDocumentElement();
NodeList childNodes = rootElement.getChildNodes();
for (int i = 0; i < childNodes.getLength();i++) {
if(childNodes.item(i) instanceof Element){
if(BEAN_ELEMENT.equals(childNodes.item(i).getNodeName())){
//解析Bean标签
Element bean = (Element) childNodes.item(i);
String id = bean.getAttribute(ID_ATTRIBUTE);
String name = bean.getAttribute(NAME_ATTRIBUTE);
String className = bean.getAttribute(CLASS_ATTRIBUTE);
Class> clazz = null;
try {
clazz = Class.forName(className);
} catch (ClassNotFoundException e) {
throw new BeansException("Cannot find class [" + className + "]");
}
//id优先于name
String beanName = StrUtil.isNotEmpty(id) ? id : name;
if (StrUtil.isEmpty(beanName)) {
//如果id和name都为空,将类名的第一个字母转为小写后作为bean的名称
beanName = StrUtil.lowerFirst(clazz.getSimpleName());
}
BeanDefinition beanDefinition = new BeanDefinition(clazz);
//Bean属性
for(int j = 0; j < bean.getChildNodes().getLength(); j++) {
if(PROPERTY_ELEMENT.equals(bean.getChildNodes().item(j).getNodeName())){
//解析property标签
Element property = (Element) bean.getChildNodes().item(j);
String nameAttribute = property.getAttribute(NAME_ATTRIBUTE);
String valueAttribute = property.getAttribute(VALUE_ATTRIBUTE);
String refAttribute = property.getAttribute(REF_ATTRIBUTE);
if (StrUtil.isEmpty(nameAttribute)) {
throw new BeansException("The name attribute cannot be null or empty");
}
Object value = valueAttribute;
if (StrUtil.isNotEmpty(refAttribute)) {
value = new BeanReference(refAttribute);
}
PropertyValue propertyValue = new PropertyValue(nameAttribute,value);
beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
}
}
if (getRegistry().containsBeanDefinition(beanName)) {
//beanName不能重名
throw new BeansException("Duplicate beanName[" + beanName + "] is not allowed");
}
//注册BeanDefinition
getRegistry().registerBeanDefinition(beanName, beanDefinition);
} }
}
}
}
@Test
public void testXmlFile() throws Exception {
DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.loadBeanDefinitions("classpath:spring.xml");
Person person = (Person) beanFactory.getBean("person");
System.out.println(person);
assertThat(person.getName()).isEqualTo("derek");
assertThat(person.getCar().getBrand()).isEqualTo("porsche");
Car car = (Car) beanFactory.getBean("car");
System.out.println(car);
assertThat(car.getBrand()).isEqualTo("porsche");
}
}
Person{name='yiHui', age='null', car=Car{name='Rolls-Royce'}}